The subject matter disclosed herein relates to X-ray tubes and, in particular, to electron beam steering within an X-ray tube.
In non-invasive imaging systems, X-ray tubes are used in fluoroscopy, projection X-ray, tomosynthesis, and computer tomography (CT) systems as a source of X-ray radiation. Typically, the X-ray tube includes a cathode and a target. A thermionic filament within the cathode emits a stream of electrons towards the target in response to heat resulting from an applied electrical current, with the electrons eventually impacting the target. A steering magnet assembly within the X-ray tube may control the size and location of the electron stream as it hits the target. Once the target is bombarded with the stream of electrons, it produces X-ray radiation.
The X-ray radiation traverses a subject of interest, such as a human patient or baggage, and a portion of the radiation impacts a detector or photographic plate where the image data is collected. In a medical diagnostic context, tissues that differentially absorb or attenuate the flow of X-ray photons through the subject of interest produce contrast in a resulting image. In some X-ray systems, the photographic plate is then developed to produce an image which may be used by a radiologist or attending physician for diagnostic purposes. In other contexts, parts, baggage, parcels, and other subjects may be imaged to assess their contents and for other purposes. In digital X-ray systems, a digital detector produces signals representative of the received X-ray radiation that impacts discrete pixel regions of a detector surface. The signals may then be processed to generate an image that may be displayed for review. In CT systems, a detector array, including a series of detector elements, produces similar signals through various positions as a gantry is displaced around a patient.
One method of imaging in CT systems includes dual energy imaging. In a dual energy application, data is acquired from an object using two operating voltages of an X-ray source to obtain two sets of measured intensity data using different X-ray spectra, which are representative of the X-ray flux that impinges on a detector element during a given exposure time. Since projection data sets corresponding to two separate energy spectra must be acquired, the operating voltage of the X-ray tube is typically switched rapidly so that the same anatomy is sampled at both high and low x-ray energy to prevent image degradation due to object motion.
For X-ray systems using the fast voltage switching methods as well as X-ray systems that have wobble capabilities, eddy currents may be induced into the beam pipe through which the electron beam passes, the core of the magnets used to steer the beam, and the windings of the steering magnet assembly. Such induction may slow response time for deflection of the electron stream, and thus may result in increased transition time and reduced exposure at a required power level. Accordingly, a need exists for improved response times within the steering magnet assembly.